Ink jet printing is a well-known technique by which printing is accomplished without contact between the printing device and the substrate on which the printed characters are deposited. Briefly described, ink jet printing involves the technique of projecting a stream of ink droplets to a surface and controlling the direction of the stream, e.g., electronically, so that the droplets are caused to form the desired printed image on that surface. This technique of noncontact printing is well-suited for application of characters onto a variety of surfaces including porous and non-porous surfaces. Ink jet printing can be accomplished in a continuous mode as well as in a drop-on-demand mode.
Reviews of various aspects of ink jet printing can be found in these publications: Kuhn et al., Scientific American, April, 1979, 162-178; and Keeling, Phys. Technol., 12(5), 196-203 (1981). Various ink jet apparatuses are described in the following U.S. Pat. Nos. 3,060,429, 3,298,030, 3,373,437, 3,416,153, and 3,673,601.
In general, an ink jet ink composition must meet one or more rigid requirements to be useful in ink jet printing operations. These relate to viscosity, resistivity, solubility, compatibility of components, and wettability of the substrate. Further, the ink must be quick-drying and smear resistant, must be capable of passing through the ink jet nozzle without clogging, and must permit rapid cleanup of the machine components with minimum effort.
In addition, the printed image should be robust and have good adhesion to the substrate. The printed image should have rub or abrasion resistance. Attempts have been made in the industry to improve these qualities by providing inks that are reactive. In many of these attempts, a reactive ink is provided which cures upon exposure to heat or UV light to provide a durable image. In these systems, the curing results in the formation of cross-links among the components of the ink. They often fail to disclose a system in which a reactive component forms a covalent bond with the printed substrate, as discussed below. For example, U.S. Pat. No. 4,978,969, discloses a method of ink jet printing using an UV curable ink composition. The ink contains an UV curable adhesive such as an urethane oligomer. The ink is jet printed onto a substrate which is then exposed to UV light to effect the curing. It is worth noting that the aforesaid UV exposure is carried out for a significantly long period of time, i.e., for about 0.5-10 minutes.
U.S. Pat. No. 5,230,733 discloses an ink composition containing a water soluble polymer-bound dye, such as a dye bound to a polymer having hydroxyl and carboxyl pendant groups, which loses water and becomes insoluble upon exposure to heat. U.S. Pat. No. 5,380,769 discloses a two-component system involving a base ink component containing a cross-linkable agent and a curing component containing a cross-linking agent. The components are applied to the receiving substrate separately. An example of a cross-linkable agent is an ethylene-acrylic acid copolymer, and an example of cross-linking agent is an amine such as diethylenetriamine. The printed image contains a product of the reaction between the cross-linkable agent and the cross-linking agent.
U.S. Pat. No. 5,738,013 discloses a method of making a lithographic plate which employs a water-insoluble printed image made by using an ink jet ink composition. The ink composition contains a liquid carrier and an organic reactive component such as a blocked isocyanate. The ink is printed on a hydrophilic receiving layer that contains a hydrophilic coating, such as a coating of polyvinyl alcohol. Upon subsequent exposure to an energy source, such as heat, a water-insoluble pattern is formed on the hydrophilic receiving layer. The printed image is then transferred to a lithographic plate. It is again worth noting that the formation of the pattern is effected under rather harsh conditions, i.e., by heating the receiving layer with a hot air gun set at 900.degree. F. and held at 18 inches from the layer for about 5 minutes.
European Patent Application 0 672 538 discloses an ink/support medium set. The ink contains an aqueous carrier and a dye or pigment dispersion as the colorant. The support medium contains a plastic support sheet and a coating layer that contains a hydrophilic polymer, for example, polyvinyl alcohol, and a reactive component, for example, one that contains acid groups. After ink jet printing, the printed medium is exposed to an energy source, such as heat or UV, and as a result of which, the hydrophilic polymer undergoes a cross-linking reaction.
U.S. Pat. No. 4,694,302 discloses a two-part ink jet printing system, for example, wherein one part of the system contains carboxymethylcellulose, which is a known reactive polymer. The second part contains an aluminum salt. The dye can be present in either part. When the two parts are deposited on a substrate, the reaction between the carboxymethylcellulose and the aluminum salt leads to the formation of a polymer lattice which binds the dye therein, thereby forming a water-fast ink. The '302 patent also discloses a one-part ink jet printing system, for example, wherein the ink contains a colloidal suspension of carbon black in diglyme solvent and a reactive species such as sebacyl chloride. Upon deposition of the ink on a cellulose-containing substrate such as paper, the sebacyl chloride reacts with the cellulose to form a cellulosic polymer.
Thus, there exists a need for a jet ink composition containing a component that is reactive to and forms a covalent bond with the receiving substrate.
Further, as discussed above, many reactive ink jet ink compositions require long curing times and/or high temperatures to complete curing. Thus, there exists a need for a jet ink composition that cures relatively fast. There also exists a need for a jet ink composition that cures at relatively low or moderate temperatures.
These and other objects of the present invention will be apparent from the detailed description of the preferred embodiments of the invention set forth below.